Five-nines is less than 10 minutes of downtime per year. I doubt anyone is really guaranteeing that without 24/7 active monitoring and maintaining extensive automated failover systems, which is already several full-time jobs. No solo operator is credibly providing that level of service.

OK, I concede that it is not completely inconceivable to do that, but unless the service you're operating is relatively light in its demands on the tech stack, I think it's a very impressive achievement to maintain infrastructure that can consistently and reliably deliver that performance on your own if you're also the person doing the development work and your infrastructure costs aren't getting silly.

We have a simple, fully redundant architecture at one of my businesses as well, and I suppose we probably do achieve five-9s most years, but I wouldn't be willing to guarantee that to customers with serious money on the line if we missed it. We're still only D disk failures at similar times away from degraded performance while we spin up new machines from scratch, or N network failures away from degraded performance until we can bring up more capacity where it's still available.

Though the promised uptime might not matter that much in practice, since the penalties for a couple of hours of downtime are often affordable.

Also, I'm not convinced that it's needed for a normal product. When my work Gmail was offline, I just had lunch early and then later it worked again.

A single founder offering higher availability than Gmail sounds like a masochist to me.